1. Field of the Invention
The present invention relates to an EGR sensor for controlling the recycled amount of an exhaust-gas of a motor vehicle.
2. Description of the Related Art
In a conventional EGR sensor, when an actuating shaft is pressed by a rod of a solenoid which drives an EGR valve of a motor vehicle, a movable member engaged with the actuating shaft moves axially, so that a slider held by the movable member is brought into sliding contact with a resistor provided on a substrate. At this time, a resistance value of the resistor changes to detect the distance of the movement of the actuating shaft (for example, refer to Japanese Unexamined Patent Application Publication No. 2002-21648).
The structure of a conventional EGR sensor will now be described with reference to a drawing. FIG. 6 is a sectional view of the conventional EGR sensor as seen from the side.
In the drawing, a case 101 has a receiving portion 101a with its one side open. An insulating substrate 103 having a resistor 102 provided thereon is received within the receiving portion 101a of the case 101 and is pressed with a spring 104 from the bottom. Further, the resistor 102 is connected to a connector pin 105 with a connecting clip 106. A cover 107 has a flat-plate-shaped base 107a, and a cylindrical bearing 107c having a hole 107b at its center. The cover is mounted on the case 101 so as to cover the opening portion of the case 101. An actuating shaft 108 has a columnar shank 108a, and a protrusion 108c extending straight, axially and rearward from the shank 108a. The shank 108a is inserted into the hole 107b of the cover 107, and the protrusion 108c is latched to the rear end of the bearing 107c. 
A slider 110 is attached to the bottom of a movable member 109, and the slider 110 is attached to the case 101 so as to be slidable in the receiving portion 101awhile it is brought in contact with the resistor 102. Detecting means comprises a variable resistor composed of the resistor 102 and the slider 110. A coil spring 111 is located in the receiving portion 101a such that its one end abuts on the rear wall 101c of the case 101 and its other end abuts on the spring receiving portion 109cof the movable member 109. The movable member 109 is forwardly urged together with the actuating shaft 108.
In the EGR sensor, when the actuating shaft 108 is pressed against a biasing force of the coil spring 111 by a rod of a solenoid, which drives an EGR valve of a motor vehicle, the movable member 109 is axially and linearly moved by the actuating shaft 108. Then, the slider 110 moves on the resistor 102. As a result, a resistance value of the resistor detected by detecting means changes so that the distance of movement of the actuating shaft 108 is detected.
Further, when the rod is released from pressing the actuating shaft 108, the movable member 109 is pushed back by the coil spring 111, and returned to its initial state.
Sufficient airtightness is required for an EGR sensor for a motor vehicle. However, since a shaft and a bearing slide relative to each other, there is a probability that a gap is formed between the shaft and the bearing, the moisture contained in an exhaust-gas enters the EGR sensor through the gap, and is then liquefied therein, and the resulting water is stagnated in a hollow part formed by the bearing and the case. There is also a problem in that a contacting portion between a clip terminal and a substrate, or a contacting portion between the clip terminal and other terminal may corrode, which damages the reliability of contact therebetween, and short-circuiting may occur between electrodes due to the water.
The above problems can be solved by arranging the bearing and the end of substrate such that they do not overlap each other in their longitudinal direction, or by causing the bearing part to protrude outwardly. However, another problems occur in that the length of a product may increase and the movable range of the actuating shaft may become short.
Accordingly, the present invention is designed to resolve above problems, and it is an object of the present invention to provide an EGR sensor capable of stably holding an actuating shaft of a product without increasing the length of the actuating shaft in its longitudinal direction and shortening the movable range of the actuating shaft, and capable of preventing the water stagnated in the EGR sensor from affecting contacting portions of conductive parts, such as electrodes or terminals.
In order to solve the above problems, as first means, the present invention provides an EGR sensor comprising: a linearly and axially movable actuating shaft, a slider driven by the actuating shaft, a substrate having a plurality of external lead-out terminals and electrode and having a slider slidable thereon, and a casing having an insertion hole through which the actuating shaft passes provided therein and having a bearing for guiding the movement of the actuating shaft and a receiving portion for receiving the substrate and the slider. When the casing is attached, the bearing is located downwardly. A communicating passage comprising a groove or a hole is provided at the side of the bearing, the communicating passage being located lower than a position where the external lead-out terminals or electrodes of the substrate received in the receiving portion are attached, and the communicating passage leading to the insertion hole from the inside of the receiving portion. The moisture stagnated in the receiving portion is drained through the communicating passage to the outside.
Further, as second means, the communicating passage is formed in a direction orthogonal to the axial direction of the actuating shaft in the bearing.
Further, as third means, the communicating passage is formed in the axial direction of the actuating shaft in the bearing.
Further, as fourth means, a plurality of the communicating passages is formed in the circumferential direction of the bearing.
Further, as fifth means, the present invention provides an EGR sensor comprises a linearly and axially movable actuating shaft, a slider driven by the actuating shaft, a substrate having a plurality of external lead-out terminals and an electrode and having a slider slidable thereon, and a casing having an insertion hole through which the actuating shaft passes provided therein and having a bearing for guiding the movement of the actuating shaft and a receiving portion for receiving the substrate and the slider. When the casing is attached, the bearing is located downwardly. A communicating passage comprising an axially extending groove is formed at the side of the actuating shaft. At a first actuating position of the actuating shaft, the communicating passage directly connects the receiving portion with the outside, so that the moisture stagnated in the receiving portion is drained through the communicating passage to the outside. At a second actuating position of the actuating shaft, the communicating passage does not directly connect the receiving portion to the outside.
Further, as the sixth means, when an engine stops and a valve closes, the actuating shaft is at the first actuating position, and when the engine is driven and the valve is operated, the actuating shaft is at the second actuating position.
As described above, an EGR sensor of the present invention comprises a linearly and axially movable actuating shaft, a slider driven by the actuating shaft, a substrate having a plurality of external lead-out terminals and electrode and having a slider slidable thereon, and a casing having an insertion hole through which the actuating shaft passes provided therein and having a bearing for guiding the movement of the actuating shaft and a receiving portion for receiving the substrate and the slider. When the casing is attached, the bearing is located downwardly. A communicating passage comprising an axially extending groove is formed at the side of the actuating shaft. At a first actuating position of the actuating shaft, the communicating passage directly connects the receiving portion with the outside, so that the moisture stagnated in the receiving portion is drained through the communicating passage to the outside. At a second actuating position of the actuating shaft, the communicating passage does not directly connect the receiving portion with the outside. Thus, the water stagnated in the EGR sensor is located lower than the external lead-out terminals or electrodes of the substrate and is drained through the communicating passage to the outside. As a result, the contacting portions can be prevented from corroding or short-circuiting without causing immersion of the external terminals or electrodes in the water.
Further, since the length of a bearing surface for receiving the actuating shaft of the bearing portion remains unchanged, the actuating shaft can be firmly held therein.
Further, the communicating passage is formed in a direction orthogonal to the axial direction of the actuating shaft in the bearing. Thus, a communicating passage is blocked by the actuating shaft at the side of the bearing. As a result, a large amount of the moisture included in an exhaust-gas does not enter the EGR sensor.
Further, the communicating passage is formed in the axial direction of the actuating shaft in the bearing. Thus, the moisture stagnated in the EGR sensor can be drained along the actuating shaft. As a result, the moisture can be surely drained to the outside.
Further, a plurality of the communicating passages is formed in the circumferential direction of the bearing. Thus, the rate at which the water is drained to the outside is rapidly performed. As a result, the level of water in the EGR sensor can be rapidly lowered and the actuating shaft can be surely held in the bearing.
Further, an EGR sensor of the present invention comprises a linearly and axially movable actuating shaft, a slider driven by the actuating shaft, a substrate having a plurality of external lead-out terminals and electrode and having a slider slidable thereon, and a casing having an insertion hole through which the actuating shaft passes provided therein and having a bearing for guiding the movement of the actuating shaft and a receiving portion for receiving the substrate and the slider. When the casing is attached, the bearing is located downwardly. A communicating passage comprising an axially extending groove is formed at the side of the actuating shaft. At a first actuating position of the actuating shaft, the communicating passage directly connects the receiving portion with the outside, so that the moisture stagnated in the receiving portion is drained through the communicating passage to the outside. At a second actuating position of the actuating shaft, the communicating passage does not directly connect the receiving portion with the outside. At the first actuating position, the water stagnated in the EGR sensor is drained through the communicating passage to the outside. Thus, the contacting portions can be prevented from corroding or short-circuiting without causing immersion of the external lead-out terminals or electrodes in the water. At the second actuating position, moisture can be refrained from entering the EGR sensor.
Further, when an engine stops and a valve closes, the actuating shaft is at the first actuating position, and when the engine is driven and the valve is operated, the actuating shaft is at the second actuating position. Thus, at the time of the operation of the valve when it is easy for water to enter the receiving portion, the communicating passage does not communicate with the inside or outside, and, at the time of closing of the valve when it is difficult for water to enter the receiving portion, the communicating passage communicates with the inside or outside. As a result, the moisture stagnated in the EGR sensor can be surely drained to the outside while the moisture in an exhaust-gas can be efficiently refrained from entering the EGR sensor.